Secondary instability mechanisms in compressible axisymmetric boundary layers
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Ng, Lian L.↗
Engineering topics
Ng, Lian L.
Publications and source records attributed to Ng, Lian L..
Secondary instabilities in compressible boundary layers
The secondary instability mechanisms in a two-dimensional (2-D) compressible boundary layer over a flat plate have been examined for a range of Mach numbers up to 4.5. For subsonic and low supersonic flows, fundamental resonance dominates when the amplitude of the (2-D) primary disturbance is high, while subharmonic resonance prevails in an environment with a low primary disturbance. At a high supersonic Mach number of 4.5, the secondary instability of the second-mode primary is stronger than that of the first-mode primary. Further, the subharmonic and the combination resonance modes, which are slightly detuned from the subharmonic, are the dominant instabilities. The influence of the propagation direction of the primary disturbance on secondary instabilities is investigated at Mach 1.6. Whereas the fundamental and the subharmonic disturbances propagate synchronously with a 2-D primary wave, this is not true for an oblique primary. A subset of the secondary instability results is verified against direct numerical simulations. Some comparisons between spatial and temporal secondary instabilities have been made at Mach 1.6.
Ng, Lian L.↗
Secondary instability mechanisms in compressible, axisymmetric boundary layers
Secondary instability mechanisms in compressible, axisymmetric boundary layers are analyzed using spectrally-accurate mean-flow and stability codes. Results show that subharmonic disturbances are the most dangerous secondary disturbances in an environment with a low to moderate intensity of the primary disturbance. The relation between spatial and temporal analyses of the secondary disturbance is explored at Mach 1.6 along a flat plate and Mach 6.8 along a cone. Spatial direct numerical simulations are utilized to confirm the quantitative predictions from spatial secondary instability theory.
Ng, Lian L.↗
The transition prediction toolkit: LST, SIT, PSE, DNS, and LES
The e(sup N) method for predicting transition onset is an amplitude ratio criterion that is on the verge of full maturation for three-dimensional, compressible, real gas flows. Many of the components for a more sophisticated, absolute amplitude criterion are now emerging: receptivity theory, secondary instability theory, parabolized stability equations approaches, direct numerical simulation and large-eddy simulation. This paper will provide a description of each of these new theoretical tools and provide indications of their current status.
Zang, Thomas A.↗
On the nonlinear stability of a high-speed, axisymmetric boundary layer
The stability of a high-speed, axisymmetric boundary layer is investigated using secondary instability theory and direct numerical simulation. Parametric studies based on the temporal secondary instability theory identify subharmonic secondary instability as a likely path to transition on a cylinder at Mach 4.5. The theoretical predictions are validated by direct numerical simulation at temporally-evolving primary and secondary disturbances in an axisymmetric boundary-layer flow. At small amplitudes of the secondary disturbance, predicted growth rates agree to several significant digits with values obtained from the spectrally-accurate solution of the compressible Navier-Stokes equations. Qualitative agreement persists to large amplitudes of the secondary disturbance. Moderate transverse curvature is shown to significantly affect the growth rate of axisymmetric second mode disturbances, the likely candidates of primary instability. The influence of curvature on secondary instability is largely indirect but most probably significant, through modulation of the primary disturbance amplitude. Subharamonic secondary instability is shown to be predominantly inviscid in nature, and to account for spikes in the Reynolds stress components at or near the critical layer.
Pruett, C. D.↗
On the nonlinear stability of a high-speed, axisymmetric boundary layer
The stability of a high-speed, axisymmetric boundary layer is investigated using secondary instability theory and direct numerical simulation. Parametric studies based on the temporal secondary instability theory identify subharmonic secondary instability as a likely path to transition on a cylinder at Mach 4.5. The theoretical predictions are validated by direct numerical simulation at temporally-evolving primary and secondary disturbances in an axisymmetric boundary-layer flow. At small amplitudes of the secondary disturbance, predicted growth rates agree to several significant digits with values obtained from the spectrally-accurate solution of the compressible Navier-Stokes equations. Qualitative agreement persists to large amplitudes of the secondary disturbance. Moderate transverse curvature is shown to significantly affect the growth rate of axisymmetric second mode disturbances, the likely candidates of primary instability. The influence of curvature on secondary instability is largely indirect but most probably significant, through modulation of the primary disturbance amplitude. Subharmonic secondary instability is shown to be predominantly inviscid in nature, and to account for spikes in the Reynolds stress components at or near the critical layer.
Pruett, C. David↗